Self-forming barrier process

ABSTRACT

A method is provided, including the following operations: performing a deposition process on a substrate, the deposition process configured to deposit a ruthenium layer in a feature on the substrate, the ruthenium layer being doped with zinc at an atomic percentage less than approximately 30 percent; after depositing the ruthenium layer, annealing the substrate, wherein the annealing is configured to cause migration of the zinc to an interface of the ruthenium layer and an oxide layer of the substrate, the migration of the zinc producing an adhesive barrier at the interface that inhibits electromigration of the ruthenium layer.

FIELD OF THE INVENTION

Implementations of the present disclosure relate to a zinc self-forminglayer, and related methods, apparatus, and systems.

DESCRIPTION OF THE RELATED ART

A typical current dual-damascene process flow involves depositing abarrier/liner layer (e.g. TaN/Ta, TiN/Ti, etc.) prior to viametallization with Cu. The barrier/liner stack improves adhesion betweenCu and oxide/low-k dielectric, and also serves to retardelectromigration. The barrier/liner also acts as a diffusion barrier forCu and is thus needed for reliability. However, the barrier/liner stackat the line/via interface is highly resistive and prevents furtherscaling as via dimensions shrink.

Currently, via pre-fill using an electroless cobalt process is beingexplored as an alternative. Although this reduces via resistancecompared to the baseline, reliability concerns still exist as there isno interfacial adhesion and diffusion barrier between cobalt andoxide/low-k dielectric. Copper via pre-fill, while technically possible,fails reliability due to poor adhesion between Cu and the dielectric.

SUMMARY

Implementations of the present disclosure provide process flows for viametallization using a M—Zn alloy, where M=Cu, Co or Ni. Metal (M) isdoped with an electronegative element (e.g. Zn at about 1 to 30 atomicpercent in some implementations; about 1 to 20 atomic percent in someimplementations; about 1 to 5 atomic percent in some implementations)which can be driven to the metal oxide interface upon heat treatmentwhere it forms a silicate diffusion barrier. This allows for back-endscaling by mitigating via resistance and via reliability which is amajor bottleneck for future technology nodes

In some implementations, a method is provided, comprising: performing adeposition process on a substrate, the deposition process configured todeposit a copper layer in a feature on the substrate, the copper layerbeing doped with zinc at an atomic percentage less than approximately 30percent; after depositing the copper layer, annealing the substrate,wherein the annealing is configured to cause migration of the zinc to aninterface of the copper layer and an oxide layer of the substrate, themigration of the zinc producing an adhesive barrier at the interfacethat inhibits electromigration of the copper layer.

In some implementations, the feature does not include a barrier layerprior to the deposition of the copper layer.

In some implementations, the annealing of the substrate causes bondingof the zinc to oxygen at the interface to form the barrier.

In some implementations, the annealing of the substrate is performed ata temperature less than approximately 350 degrees Celsius.

In some implementations, the deposition process is defined by anelectroless deposition process configured to co-deposit copper and zinc.

In some implementations, the feature is a via, and wherein the methoddefines a pre-fill operation configured to partially fill the via withthe copper layer.

In some implementations, the interface of the copper layer and the oxidelayer is defined along a sidewall of the via.

In some implementations, a method is provided, comprising: performing adeposition process on a substrate, the deposition process configured todeposit a metallic layer in a feature on the substrate, the metalliclayer consisting of one or more of copper, cobalt, or nickel, andwherein the metal layer is doped with zinc at an atomic percentage lessthan approximately 5 percent; after depositing the metallic layer,annealing the substrate, wherein the annealing is configured to causemigration of the zinc to an interface of the metallic layer and an oxidelayer of the substrate, the migration of the zinc producing a barrier atthe interface that inhibits electromigration of the metallic layer.

In some implementations, the feature does not include a barrier layerprior to the deposition of the metallic layer.

In some implementations, the annealing of the substrate causes bondingof the zinc to oxygen at the interface to form the barrier.

In some implementations, the annealing of the substrate is performed ata temperature less than approximately 350 degrees Celsius.

In some implementations, the deposition process is defined by anelectroless deposition process.

In some implementations, the feature is a via, and wherein the methoddefines a pre-fill operation configured to partially fill the via withthe metallic layer.

In some implementations, the interface of the metallic layer and theoxide layer is defined along a sidewall of the via.

In some implementations, a method is provided, comprising: performing afirst deposition process on a substrate, the first deposition processconfigured to deposit a copper layer in a feature on the substrate;performing a second deposition process on the substrate, the seconddeposition process configured to deposit a conformal layer of zinc overthe copper layer; annealing the substrate, wherein the annealing isconfigured to cause migration of the zinc to an interface of the copperlayer and an oxide layer of the substrate, the migration of the zincproducing a barrier at the interface that inhibits electromigration ofthe copper layer.

In some implementations, the feature does not include a barrier layerprior to the deposition of the copper layer.

In some implementations, the annealing of the substrate causes bondingof the zinc to oxygen at the interface to form the barrier.

In some implementations, the annealing of the substrate is performed ata temperature less than approximately 350 degrees Celsius.

In some implementations, the first deposition process is defined by anelectroless deposition process configured to deposit copper.

In some implementations, the feature is a via, and wherein the methoddefines a pre-fill operation configured to partially fill the via withthe copper layer.

In some implementations, the interface of the copper layer and the oxidelayer is defined along a sidewall of the via.

In some implementations, a method is provided, comprising: performing anelectrochemical atomic layer deposition (eALD) process on a substrate,the eALD process configured to deposit a conformal copper seed layer ina feature on the substrate, the copper seed layer being doped with zincat an atomic percentage less than approximately 5 percent; depositing acopper fill over the copper seed layer; after depositing the copperfill, annealing the substrate, wherein the annealing is configured tocause migration of the zinc to an interface of the copper seed layer andan oxide layer of the substrate, the migration of the zinc producing abarrier at the interface that inhibits electromigration of the copper.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 conceptually illustrates a via/interconnect having various layersof material deposited therein, in accordance with implementations of thedisclosure.

FIG. 2A illustrates a process demonstrating formation of a zincself-forming barrier on a blanket ruthenium liner on a thermal oxidewafer, in accordance with implementations of the disclosure.

FIG. 2B illustrates a series of STEM EDS (scanning transmission electronmicroscopy; energy-dispersive x-ray spectroscopy) maps showing thepresence of elemental copper, ruthenium, and zinc in the sampleprocessed in accordance with the implementation of FIG. 2A, inaccordance with implementations of the disclosure.

FIG. 2C is an electron energy loss spectroscopy (EELS) profile of thesample processed in accordance with the implementations of FIGS. 2A and2B, in accordance with implementations of the disclosure.

FIG. 3 illustrates adhesion testing of substrates processed according tovarious methods, in accordance with implementations of the disclosure.

FIGS. 4A and 4B are graphs showing concentration of various elements asa function of depth to study copper diffusion, in accordance withimplementations of the disclosure.

FIGS. 5A and 5B illustrate a process flow for preparation of asubstrate, and the results of analysis thereof by XPS (x-rayphotoelectron spectroscopy), in accordance with implementations of thedisclosure.

FIGS. 6A-D illustrate a process flow for preparation of a substrate, andcorresponding orbital scan results, in accordance with implementationsof the disclosure.

FIG. 7 conceptually illustrates an eALD process using two separatebaths, in accordance with implementations of the disclosure.

FIG. 8 is a graph conceptually illustrating a potential driven eALDprocess, in accordance with implementations of the disclosure.

FIGS. 9A-D conceptually illustrate a process flow for Zn-based viametallization, in accordance with implementations of the disclosure.

FIGS. 10A-D conceptually illustrate a process flow for Zn-based viametallization, in accordance with implementations of the disclosure.

FIGS. 11A-D illustrate a process flow for barrier formation andpre-fill, in accordance with implementations of the disclosure.

FIGS. 12A-F illustrate a process for generating a self-formingzinc-based barrier in a via, in accordance with implementations of thedisclosure.

FIGS. 13A-C illustrate a process for generating a self-formed adhesionlayer for ruthenium metallization of a via, in accordance withimplementations of the disclosure.

FIGS. 14A-D illustrate a process for generating a self-forming adhesionlayer for ruthenium metallization, in accordance with implementations ofthe disclosure.

FIG. 15 shows a control module for controlling the systems describedabove, in accordance with implementations of the disclosure.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth toprovide a thorough understanding of the presented embodiments. Thedisclosed embodiments may be practiced without some or all of thesespecific details. In other instances, well-known process operations havenot been described in detail to not unnecessarily obscure the disclosedembodiments. While the disclosed embodiments will be described inconjunction with the specific embodiments, it will be understood that itis not intended to limit the disclosed embodiments.

In keeping with Moore's Law, there has been a continual drive towardssmaller and smaller feature sizes in the semiconductor industry. Atpresent, semiconductor manufacturers are commonly producing devices witha 28 nanometer (nm) feature size, or approximately 28 nm pitch. Deviceswith a 36 nm pitch size are expected to soon. Typically, the pitch ishalved every two technology nodes. Thus, it is expected that withinabout two to three nodes, devices will be at an 18 nm pitch, or about 10nm feature size or less.

However, as pitch and feature dimensions shrink, so resistance begins toplay a larger role in circuit performance. This is attributable to acouple of effects as device features shrink. First, the conductorshrinks when feature sizes a reduced, thereby increasing the resistance.And second, the resistive impact of layers and materials other than theconductor may become more pronounced as feature sizes shrink. This canbe due to the fact that in smaller features, the non-conductor materialsoccupy an increased proportion of the available feature volume relativeto that of the conductor material. This can be especially true in thecase of a via or interconnect structure.

FIG. 1 conceptually illustrates a via/interconnect having various layersof material deposited therein, in accordance with implementations of thedisclosure. In the illustrated example, the via 10 has an approximate 10nm feature size (20 nm pitch) and has been processed according to aconventional approach for via fill. The via 10 is patterned in adielectric material 12 of a substrate, such as an oxide or high-kdielectric material, so as to reach an underlying conductor 14. First, abarrier layer 16 (e.g. TiN, TaN, WN, etc.) is deposited in the via, toprevent diffusion and electromigration of the via conductor 22. Becauseof poor adhesion between the barrier layer 16 and the conductivematerial (e.g. Cu) of the later deposited via conductor 22, a linerlayer 18 (e.g. Ti, Ta, W, etc.) is deposited over the barrier layer 16to promote adhesion. Next, a seed layer 20 of the conductive material(e.g. Cu) is deposited over the liner layer 18. The seed layer istypically deposited by a CVD, PVD, or ALD process so as to form aconformal layer and to provide nucleation sites for bulk deposition.Then the bulk deposition/fill (e.g. typically by electroplating) of theconductive material is deposited to form the conductor 22.

However, as conceptually demonstrated by FIG. 1, this typical processscales poorly for small feature sizes such as 10 nm. For the barrier andseed layers consume a significant amount of the cross-sectional space inthe via 10, leaving little room for the actual conductor 22. This can beproblematic from a processing standpoint as the narrow available spacefor fill increases the likelihood of the formation of voids during thefill deposition process. Further, the narrow conductor at small featuresizes increases the resistance. Also, the barrier layer 16 acts as aresistive contact between the via structure and the underlying conductor14. As can be seen, the issue of high resistance is problematic whenextending current processes to small feature sizes, as the increasedresistance will degrade device performance.

Thus, it would be desirable to enable an interconnect process thatprovides for a structure consisting of predominantly conductive materialto minimize the resistance of the conductor, with a thin barrier that isselectively deposited on the sidewalls only. A metallic contact isdesired to act as a flux divergence layer to prevent electromigration.

Implementations of the present disclosure provide methods and systems toaddress the problems described above which are inherent to conventionalprocesses when extended to 10 nm feature sizes. Broadly speaking, it hasbeen discovered that a low temperature anneal of a zinc-doped conductivelayer in an interconnect structure causes the zinc to migrate to theinterface with the oxide and form a (self-forming) barrier that preventselectromigration and diffusion of copper, while also improving adhesion.The zinc-doped conductive layer can be deposited by an electrochemicalALD process that provides for conformal coverage.

FIG. 2A illustrates a process demonstrating formation of a zincself-forming barrier on a blanket ruthenium liner on a thermal oxidewafer, in accordance with implementations of the disclosure.

As indicated at reference 30, initially, a 3 nm Ru layer is depositedover a 100 nm (thermal) SiO₂ layer. This is further shown by the TEMimage 36, which shows the ruthenium layer 38 over the thermal oxidelayer 40.

An electrochemical ALD process was performed to deposit a 2 nm layer ofzinc-doped copper (CuZn layer), followed by an electroless bulkdeposition of a 60 nm layer of copper, resulting in the stack shown atreference 32. This is further shown by the TEM image 42, illustratingthe Cu layers at reference 44, positioned over the ruthenium layer 46and the oxide layer 48.

Next the substrate is annealed at a temperature of 360 degrees Celsiusfor 30 minutes. This results in a stack as shown at reference 34,wherein the zinc migrates to the interface between the ruthenium and theoxide layers. This is further shown in the TEM image 50, of which anexpanded portion is shown at reference 52. In the image 52, the copperlayer 54 is seen over the ruthenium layer 56. With a zinc-containingbarrier layer 58 now formed at the interface of the ruthenium layer 56with the oxide layer 60.

FIG. 2B illustrates a series of STEM EDS (scanning transmission electronmicroscopy; energy-dispersive x-ray spectroscopy) maps showing thepresence of elemental copper, ruthenium, and zinc in the sampleprocessed in accordance with the implementation of FIG. 2A, inaccordance with implementations of the disclosure. The various EDS maps70, 74, and 78 are horizontally aligned to show the relative depths ofvarious corresponding elements. The EDS map 70 shows the presence ofcopper in an upper layer 72. The EDS map 74 shows the presence ofelemental ruthenium disposed, as expected, along a layer 76 just belowthe copper layer 72. However, the EDS map 78 illustrates the presence ofzinc primarily in a layer 80 that is below the ruthenium layer 76,despite being originally deposited above the ruthenium layer.

Thus, it can be seen from these results that though the zinc wasinitially deposited in conjunction with copper over the ruthenium layer,upon the application of the anneal, the zinc in fact migrates throughthe ruthenium layer to the interface of the ruthenium with the oxide. Inthis manner, a self-forming barrier is formed by the zinc migration toand accumulation at this interface. Without being bound by anyparticular theory, it is believed that zinc exhibits an affinity for theoxide, migrating upon anneal and possibly becoming covalently to theoxygen atoms in the thermal silicon dioxide species at the interface.

FIG. 2C is an electron energy loss spectroscopy (EELS) profile of thesample processed in accordance with the implementations of FIGS. 2A and2B, in accordance with implementations of the disclosure. The plot shownillustrates a depth profile of an approximately 40 nm thickness spanningthe copper, ruthenium, zinc, and silicon dioxide layers. The atomicpercentage of copper as a function of depth is shown by the curve 90,the atomic percentage of ruthenium by the curve 92, the atomicpercentage of zinc by the curve 94, the atomic percentage of oxygen bythe curve 96, and the atomic percentage of silicon by the curve 98. Asindicated by the various profiles, there is no copper diffusion throughthe ruthenium-zinc interface into the silicon dioxide. This issignificant as it demonstrates the diffusion-inhibiting property of thezinc-containing barrier at the interface of Ru and SiO₂.

FIG. 3 illustrates adhesion testing of substrates processed according tovarious methods, in accordance with implementations of the disclosure.As indicated by the stack 100, a first sample was processed to have a100 nm SiO₂ layer, a 3 nm Ru layer, and a copper layer greater than 500nm. To perform the adhesion testing, samples were scratched with adiamond scribe, and then subjected to a tape test in order to testadhesion. As shown in the image 102, this sample failed the peel test,exhibiting delamination of the copper and ruthenium layers from thesubstrate sample. Thus, ruthenium directly on SiO₂ does not exhibitsuitable adhesion.

A second sample was processed so as to have a structure as shown by thestack 104, including a 100 nm thermal oxide layer, a 3 nm rutheniumlayer, a 2 nm layer of CuZn (deposited via eALD), and a >500 nm layer ofCu. It will be appreciated that a low temperature anneal was performedto effect migration of the zinc to the interface of the ruthenium withthe thermal oxide layer. The result of the adhesion test on this secondsample is reflected in the image 106. As shown, adhesion of ruthenium toSiO₂ is improved by the presence of the zinc barrier layer. Furthermore,additional dopant (zinc) for CMP adhesion and barrier performance wasprovided through a CuZn overburden layer.

A third sample was processed as shown by the stack 108, including alow-k 3.0 dielectric, optionally with a 3 angstrom TiN layer, a 3 nm Rulayer, a 2 nm CuZn layer (deposited via eALD), and a >500 nm copperlayer. A low temperature anneal was performed. The result of theadhesion test is shown in the image 110, and demonstrates that the zincself-forming barrier also improves adhesion of ruthenium to a low-kdielectric material. Furthermore, additional dopant (zinc) for CMPadhesion and barrier performance was provided through a CuZn overburdenlayer.

FIGS. 4A and 4B are graphs showing concentration of various elements asa function of depth to study copper diffusion, in accordance withimplementations of the disclosure. A backside SIMS (secondary ion massspectrometry) analysis was carried out on substrates processed with andwithout a CuZn layer. The backside SIMS technique is useful for studyingdiffusion of an element as it enables detection of trace amounts ofelements by depth profiling from the back side of the substrate.

With reference to FIG. 4A, a depth profile is shown for a substratehaving a PVD Cu layer over a Ru layer, over a SiO₂ layer. A 30 minuteanneal at 350 C was performed. As shown, the Cu was found to havepenetrated through the Ru layer and diffused into the SiO₂ to an extentof about 4.7 nm.

By contrast, with reference to FIG. 4B, a depth profile is shown for asubstrate having a 100 nm PVD Cu layer, over a 200 nm CuZn layer, over a3 nm Ru layer, over a SiO₂ layer. A 30 minute anneal at 350 C wasperformed. As shown by the depth profile, copper diffusion through Ruinto SiO₂ was blocked, thus demonstrating both the formation andeffectiveness of a barrier to inhibit diffusion.

FIGS. 5A and 5B illustrate a process flow for preparation of asubstrate, and the results of analysis thereof by XPS (x-rayphotoelectron spectroscopy), in accordance with implementations of thedisclosure. As indicated at reference 130 of FIG. 5A, initially, acopper stack consisting of 100 nm Cu and 200 nm of CuZn (Zn at 1 atomicpercent) was deposited over a 3 nm Ru layer, over a 50 nm layer ofthermal oxide. Then a forming gas anneal was performed at 350 C. Asindicated at reference 132, this results in the formation of a zincself-forming barrier at the interface of the Ru and the oxide. Then, inpreparation for XPS analysis, a Cu wet etch was performed to remove thecopper-containing layers and expose the ruthenium layer, as indicated bythe structure as shown at reference 134. This structure was thencharacterized by XPS analysis.

FIG. 5B illustrates the XPS results for the foregoing sample, showingatomic percentages of Cu and Zn as a function of sputter time, which isindicative of depth. The depth of the ruthenium layer is indicated bythe shaded region 140. As shown, the atomic percentage of Zn is in factgreater than the atomic percentage of Cu at profile depths greater than(below) the Ru layer. This indicates that the zinc has migrated throughthe ruthenium layer to the interfacial region of the thermal oxide withthe ruthenium. This also suggests that the zinc that has migrated isacting as a barrier to prevent diffusion of the copper into the thermaloxide.

FIGS. 6A-D illustrate a process flow for preparation of a substrate, andcorresponding orbital scan results, in accordance with implementationsof the disclosure. With reference to FIG. 6A, the illustrated processflow was carried out to obtain a zinc self-formed barrier for analysis.As indicated by the structure shown at reference 150, initially a 100 nmCu layer and a 200 nm CuZn (Zn at one atomic percent) were depositedover a 50 nm layer of thermal oxide. Then, a forming gas anneal at 350 Cwas performed, causing migration of zinc to the oxide-copper interfaceto form a Zn self-forming barrier, as shown by the structure atreference 152. Then a wet etch was performed to remove thecopper-containing layers, exposing the zinc barrier, as shown by thestructure at reference 154.

FIGS. 6B-D are graphs showing the results of XPS analysis for specificorbital peaks of the various elements. FIG. 6B demonstrates that the Zn2 p orbital peak has been positively shifted from what would be expectedfor purely elemental Zn, meaning that the zinc has undergone oxidation.FIG. 6C demonstrates that the Si 2 p orbital peak has not shifted fromits expected value in the +4 oxidation state. FIG. 6D demonstrates thatthe O 1 s orbital peak exhibits some negative broadening suggesting thatsome of the oxygen is being reduced. In sum, it is shown that zinc isbeing oxidized, silicon is not being reduced, and there is evidence thatsome oxygen is being reduced. Thus, without being bound by anyparticular theory of explanation, it is believed that zinc is bound tooxygen at the thermal oxide interface, possibly through covalentbonding, and that this forms the structure of the self-formed barrier.

As noted herein, implementations of the present disclosure employ anelectrochemical atomic layer deposition (eALD) process. FIG. 7conceptually illustrates an eALD process using two separate baths, inaccordance with implementations of the disclosure. Electrochemical ALDis typically an atmospheric wet process used to deposit conductivemetallic films. Substrate materials are typically transition/noblemetals. With reference to FIG. 7, a substrate ‘S’ is placed in a firstbath, whereupon a monolayer of a sacrificial metal ‘M’ is adsorbed onthe substrate. Then the substrate is placed into a second bath,whereupon a depositing metal ‘N’ displaces the sacrificial metal ‘M’ onthe substrate surface. Both reactions are self-limiting and thereforemonolayer selectivity and deposition control is achieved.

While the above-described eALD process employs two separate baths, insome implementations, eALD is performed in a single bath. FIG. 8 is agraph conceptually illustrating a potential driven eALD process, inaccordance with implementations of the disclosure. Broadly speaking,eALD in a single bath is enabled by potential pulsing, to selectivelypromote the two phases of the deposition process. During a first phaseor time ‘t_(upd)’ the potential is held at a level that promotesmonolayer adsorption of the sacrificial metal ‘M’ on the substrate whileavoiding bulk deposition. This is referred to as an underpotentialdeposition. Following this, during second phase or time ‘t_(SLRR)’ thepotential is raised to a level that promotes a self-limiting redoxreplacement of the sacrificial metal ‘M’ with the depositing metal ‘N.’At the conclusion of this phase, the potential is reduced to initiatethe next cycle. In this manner, eALD in a single bath is enabled bysequentially pulsing the potential. Co-deposition at the cathodicpotential is prevented by kinetically retarding the depositing metalplating reaction.

As noted, implementations of the present disclosure provide for thedeposition of a zinc-doped copper film. This can be accomplished byeALD, wherein the sacrificial metal is zinc, and the depositing metal iscopper. The eALD process is configured so that incomplete replacement ofzinc with copper occurs during the redox replacement phase, resulting ina conformal copper film that is doped with a certain amount of zinc(e.g. about one to five atomic percent in some implementations; aboutone to 20 atomic percent in some implementations; about one to 30 atomicpercent in some implementations).

Through growth and characterization studies, it has been found that thegrowth rate of eALD copper on planar ruthenium is approximately 0.8 to 1angstrom of thickness per cycle, which translates to about a third of amonolayer per eALD cycle. It is believed that anion co-adsorption andincomplete self-limiting redox replacement prevents full monolayercoverage in a single cycle.

In sum, as noted above, an eALD process can be configured to incorporatea certain percentage of zinc into a conformal copper film. It should benoted that upon formation of the film, in the presence of oxygen, thenthe zinc will tend to migrate to the exposed surface and passivate theeALD Cu film. However, in the absence of oxygen or absent exposure tooxygen (e.g. via an additional layer to prevent exposure) the zinc willremain in the Cu film. Upon the performance of an anneal, typically in areducing environment, the zinc will migrate to an underlying oxideinterface and form a self-forming barrier. This migration can includemovement of the zinc through underlying metallic layers such as througha ruthenium layer to the ruthenium-oxide interface. There is evidence ofa reaction of the zinc with the oxide at the interface, providingimproved adhesion properties. Furthermore, the self-forming barrierdefined by the zinc inhibits Cu migration through the oxide. This hasbeen demonstrated with a 1% Zn doped film of CuZn at 2 nm thickness.

In view of the foregoing, various process flows are contemplated for viametallization using a M—Zn alloy, where M=Cu, Co or Ni. Metal (M) isdoped with an electronegative element (such as Zn, 1-5 at.%) which canbe driven to the metal oxide interface upon heat treatment where itforms a silicate diffusion barrier. This allows for back-end scaling bymitigating via resistance and via reliability which is a majorbottleneck for future technology nodes.

Implementations of the present disclosure address the via resistance andreliability issues. Specifically, implementations of the presentdisclosure provide a pathway for enabling Cu via pre-fill which yieldslower via resistance than cobalt.

Furthermore, via reliability which prevented implementation of Cu viapre-fill is addressed by the Zn self-forming barrier/adhesion layer.This adhesion layer between Cu and dielectric retards electromigration,improving reliability.

Implementations of the disclosure also improve electromigration,diffusion and adhesion characteristics of electroless cobalt or nickelvia pre-fill flow. Zinc doped in cobalt or nickel diffuses to themetal/dielectric interface creating an adhesive layer which retardsmetal diffusion and electromigration.

Doping of the metal fill with approximately 1-5% Zn, e.g. via eALD, hasbeen performed, and the mobility of Zn in the Cu matrix has beendiscovered. It has been found that the direction of Zn mobility can becontrolled such that Zn is driven to the oxygen interface, through theliner (e.g. Ru) to the liner/oxide interface by heating in a reducingenvironment where it forms a silicate barrier. These observations allowseveral integration flows for via metallization using Cu, Co or Ni dopedwith Zn.

FIGS. 9A-D conceptually illustrate a process flow for Zn-based viametallization, in accordance with implementations of the disclosure. Inthe illustrated implementation, Zn is doped using an electrolessco-deposition process for M-Zn with Zn content ranging from about 1 to 5atomic percent (or about 1 to 20 or 30 atomic percent in someimplementations). Shown at FIG. 9A is a cross section of a portion of asubstrate having an etched via 165 prior to fill processing. The via 165is configured to enable formation of an interconnect to an underlyingcopper line 160. The via 165 has been etched from a dielectric layer164, and an etch stop layer and/or capping layer has been etched/removedfrom the bottom of the via, to expose the copper line 160.

With reference to FIG. 9B, a pre-fill operation is performed byelectroless deposition, so as to (partially) fill the via 165 with aM-Zn material to form a pre-fill layer 166. It will be appreciated thatin various implementations, the metal M can be a conductive metal suchas copper, cobalt, nickel, etc. or an alloy. The M-Zn material includeszinc at a concentration of about 1 to 5 atomic percent (or about 1 to 20or 30 atomic percent in some implementations). The pre-fill operationfills the bottom portion of the via 165, effectively reducing the aspectratio of the feature.

Following the pre-fill operation, an anneal is performed, which causesthe zinc to migrate to the interface of the pre-fill layer with thedielectric along the sidewalls of the via. With reference to FIG. 9C, azinc-based barrier/adhesion layer 168 is thereby formed at thedielectric interface.

Following these operations, as the aspect ratio of the via has beeneffectively reduced, in accordance with implementations of thedisclosure as shown with reference to FIG. 9D, then a conventionaldual-damascene process flow may be employed. Such a dual-damasceneprocess flow may initiate with deposition of a barrier/liner 170,providing conformal coverage over the dielectric and the pre-fill layer166.

FIGS. 10A-D conceptually illustrate a process flow for Zn-based viametallization, in accordance with implementations of the disclosure.FIG. 10A illustrates a cross section of a portion of a substrate havingan etched via 165 prior to being filled, so as to enable connection toan underlying conductor line 160.

With reference to FIG. 10B, a via pre-fill operation is performed,partially filling the via 165 with a conductive material (e.g. Cu, Co,Ni, etc. or an alloy) to form a pre-fill layer 180. In someimplementations, the conductive material of the pre-fill layer 180 is apure or substantially pure metal, that is not doped with zinc. In someimplementations, the pre-fill operation is performed via an electrolessdeposition process. In other implementations, the pre-fill operation isperformed via other deposition processes.

Subsequent to the via pre-fill operation, a conformal layer of zinc, ora layer having a high concentration of zinc (e.g. about 20 atomicpercent zinc or greater), is deposited over the via, as indicated atFIG. 10C, forming a zinc layer 182. Then a heat treatment or annealoperation is performed. This causes at least some of the zinc to bedriven through the metal pre-fill layer 180 to the metal-dielectricinterface, where it forms a zinc based barrier/adhesion layer 184, asshown at FIG. 10D.

Though in the foregoing implementation, it is generally contemplatedthat the pre-fill is not doped with zinc, in some other implementations,the pre-fill metal is doped with zinc. The subsequently depositedconformal zinc layer 182 thus provides additional zinc for the formationof the barrier/adhesion layer, and provides for formation of the zincbarrier/adhesion layer along other regions of the dielectric additionalto the metal-dielectric interface regions.

Subsequent to the process flow of the instant implementation, adual-damascene process flow can be performed.

FIGS. 11A-D illustrate a process flow for barrier formation andpre-fill, in accordance with implementations of the disclosure. As inthe foregoing implementations, at FIG. 11A, the etched via 165 is shown.Then, as shown at FIG. 11B, a conformal or semi-conformal layer 190 ofZn is deposited first in the via 165. Subsequently, a heat treatment oranneal is performed that promotes reflow and formation of theself-forming barrier/adhesion layer 192, as shown at FIG. 11C. Then, asshown at FIG. 11D, via prefill is performed in the subsequent step by adeposition process such as electroless deposition, to deposit a pre-filllayer 194 of conductive material in the via 165.

Subsequent to the process flow of the instant implementation, adual-damascene process flow can be performed.

The above-described implementations of the present disclosure addressthe issues of diffusion and poor adhesion of via pre-fill layers byproviding a self-forming barrier/adhesion layer that is minimallyconsumptive of the available via width. This maximizes the volume of thepre-fill conductive material while addressing the aforementioned issues,thereby reducing resistance of the via structure and improving deviceperformance.

In some implementations, the process flow for barrier/adhesion layerformation and pre-fill is enabled by wet deposition processes, such aselectrochemical plating and/or electroless deposition.

Since the formation of the Zn-based adhesion layer is important inaccordance with the presently described process flows, process equipmentcould utilize heating hardware in combination with wet depositionhardware (e.g. RTA, flash anneal, etc.).

FIGS. 12A-E illustrate a process for generating a self-formingzinc-based barrier in a via, in accordance with implementations of thedisclosure. With reference to FIG. 12A, after performance of etch andclean processes, a cross section of a via 165 that has been etched froma dielectric 164 is shown. The via 165 is configured to enableconnection to an underlying conductor 160, that consists of a conductivematerial such as copper. An etch stop layer 162 has been removed at thebottom of the via, exposing the underlying conductor 160 for contactwith subsequently deposited material.

With reference to FIG. 12B, a via pre-fill operation is performed, todeposit in the via 165 a pre-fill layer 180 consisting of a conductivematerial (e.g. Cu, Co, alloy, etc.). The pre-fill operation isconfigured to partially fill the via 165, so that the pre-fill layer 180occupies a bottom portion of the via 165.

With reference to FIG. 12C, a ruthenium liner 200 is deposited over thevia. In some implementations, the Ru liner 200 is deposited to have athickness in the range of about 1 to 3 nm; in some implementations, 1 to2 nm. The Ru liner 200 is deposited by a conformal deposition method,e.g. CVD, ALD, electroplating. The Ru liner 200 provides a boundary tothe conductors which it is adjacent to, acting as a flux divergencelayer and inhibiting electromigration.

With reference to FIG. 12D, a copper-zinc (CuZn) seed layer 202 isdeposited by electrochemical ALD (eALD). The CuZn seed layer 202 isprincipally a copper seed layer doped with a small percentage of zinc.In some implementations, the CuZn layer 202 is deposited to have athickness in the range of about 2 to 3 nm. Further, in someimplementations, the amount of zinc in the Cu-Zn layer 202 is in therange of about 1 to 5 atomic percent. It will be appreciated that theeALD process is specifically configured to incorporate zinc in the filmat the chosen atomic percentage.

With reference to FIG. 12E, a copper fill operation is performed, todeposit a copper fill layer 204 over the via. The copper fill operationis performed via electrochemical plating, electroless deposition, oranother deposition method suitable for bulk deposition of copper. Insome implementations, optionally, an additional CuZn overburden layer205 is deposited over the copper fill layer 204 (e.g. via eALD,electrochemical plating, or electroless deposition). The additional CuZnoverburden layer 205 is configured to provide additional zinc for thepurpose of generating the zinc self-formed barrier/adhesion layer.

In some implementations, a reflow operation is performed instead of, orin addition to, the cupper fill operation noted above. The reflowoperation can be configured to cause reflow of the CuZn seed layer 202,and/or the Cu fill layer 204.

With reference to FIG. 12F, a heat treatment or anneal operation isperformed. This causes the zinc present in the CuZn seed layer, andoptionally in the CuZn overburden layer if present, to be driven throughthe metallic layers to the oxide dielectric, where it reacts to form theself-formed barrier/adhesion layer 206. In some implementations, theanneal is performed at a temperature less than about 350 C. In someimplementations, the anneal is performed at a temperature between about40 and 450 C; in some implementations, between about 75 to 200 C; insome implementations, between about 75 to 150 C; in someimplementations, about 150 C; in some implementations, between about 250to 400 C; in some implementations, between about 300 to 350 C. In someimplementations, the anneal is performed for a time of about 2 to 30minutes; in some implementations, about 3 to 10 minutes; in someimplementations, about 5 minutes. In some implementations, a flashanneal is performed, which achieves annealing very rapidly, on the orderof milliseconds.

In some implementations, a two-part anneal process is employed, whereina first anneal is performed at a first comparatively lower temperature(e.g. 50 to 100 C in some implementations), followed by a second annealperformed at a second comparatively higher temperature (e.g. 200 to 350C in some implementations). Because copper can also migrate underannealing conditions, a single anneal of sufficiently high temperaturemay undesirably enable some copper to migrate into the dielectric beforezinc migrates sufficiently to prevent this. However, as zinc migratessignificantly faster than copper at lower temperatures, then a first lowtemperature anneal can be configured to enable at least a portion of thezinc to migrate to the interface with the dielectric before copperreaches the dielectric. Then a second comparatively higher temperatureanneal speeds the migration process of the remaining zinc, without riskof copper diffusing into the dielectric.

In some implementations, the zinc mobility described herein can beleveraged to enable other types of metallization. For example, rutheniumis known to possess desirable properties in terms of diffusion andelectromigration, thereby theoretically obviating the need for barrierlayers to address these issues as in other metallization materials suchas copper. However, poor adhesion of ruthenium to other materialsremains a challenge and has limited the potential application ofruthenium for metallization. Implementations of the present disclosureimprove adhesion of ruthenium to oxide-containing dielectric through theformation of a self-formed adhesion layer, as described below.

FIGS. 13A-C illustrate a process for generating a self-formed adhesionlayer for ruthenium metallization of a via, in accordance withimplementations of the disclosure. FIG. 13A illustrates a cross sectionof a portion of a substrate showing an etched via 165 from a dielectric164, that is configured to enable connection to an underlying conductor160.

With reference to FIG. 13B, a deposition process is performed to deposita layer 210 of ruthenium that is doped with zinc. The deposition isconfigured to fill the via 165, and may be performed via eALD in someimplementations. In some implementations, the quantity of zinc presentin the layer 210 is approximately 1 to 5 atomic percent. In someimplementations, the quantity of zinc present in the layer 210 isapproximately 1 to 20 or 30 atomic percent. Subsequently, an anneal orheat treatment operation is performed to drive the zinc to thedielectric interface. As shown at FIG. 13C, this results in formation ofa self-formed zinc-based adhesion layer 212 at the interface between theruthenium layer 210 and the dielectric 164. The adhesion layer 212improves the adhesion of the ruthenium to the dielectric, therebyimproving device reliability.

FIGS. 14A-D illustrate a process for generating a self-forming adhesionlayer for ruthenium metallization, in accordance with implementations ofthe disclosure. FIG. 14A illustrates a portion of a substrate having avia 165, following etch and clean processing. Then a rutheniumdeposition process is performed, so as to deposit a layer 220 ofruthenium in the via 165, as shown at FIG. 14B.

Subsequently, with reference to FIG. 14C, a layer 222 of zinc isdeposited over the layer 220. Then an anneal or heat treatment processis performed, causing the zinc to migrate through the ruthenium layer tothe dielectric interface, where it forms a self-forming adhesion layer224. The adhesion layer 224 provides for improved adhesion between theruthenium and the dielectric, thus improving device reliability.

FIG. 15 shows a control module 800 for controlling systems forperforming operations described above, in accordance withimplementations of the disclosure. For instance, the control module 1500may include a processor, memory and one or more interfaces. The controlmodule 1500 may be employed to control devices in the system based inpart on sensed values. For example only, the control module 1500 maycontrol one or more of valves 1502, filter heaters 1504, pumps 1506, andother devices 1508 based on the sensed values and other controlparameters. The control module 1500 receives the sensed values from, forexample only, pressure manometers 1510, flow meters 1512, temperaturesensors 1514, and/or other sensors 1516. The control module 1500 mayalso be employed to control process conditions during reactant deliveryand plasma processing. The control module 1500 will typically includeone or more memory devices and one or more processors.

The control module 1500 may control activities of the reactant deliverysystem and plasma processing apparatus. The control module 1500 executescomputer programs including sets of instructions for controlling processtiming, delivery system temperature, pressure differentials across thefilters, valve positions, mixture of gases, chamber pressure, chambertemperature, wafer temperature, RF power levels, wafer ESC or pedestalposition, and other parameters of a particular process. The controlmodule 1500 may also monitor the pressure differential and automaticallyswitch vapor reactant delivery from one or more paths to one or moreother paths. Other computer programs stored on memory devices associatedwith the control module 1500 may be employed in some embodiments.

Typically there will be a user interface associated with the controlmodule 1500. The user interface may include a display 1518 (e.g. adisplay screen and/or graphical software displays of the apparatusand/or process conditions), and user input devices 1520 such as pointingdevices, keyboards, touch screens, microphones, etc.

Computer programs for controlling delivery of reactant, plasmaprocessing and other processes in a process sequence can be written inany conventional computer readable programming language: for example,assembly language, C, C++, Pascal, Fortran or others. Compiled objectcode or script is executed by the processor to perform the tasksidentified in the program.

The control module parameters relate to process conditions such as, forexample, filter pressure differentials, process gas composition and flowrates, temperature, pressure, plasma conditions such as RF power levelsand the low frequency RF frequency, cooling gas pressure, and chamberwall temperature.

The system software may be designed or configured in many differentways. For example, various chamber component subroutines or controlobjects may be written to control operation of the chamber componentsnecessary to carry out the inventive deposition processes. Examples ofprograms or sections of programs for this purpose include substratepositioning code, process gas control code, pressure control code,heater control code, and plasma control code.

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, it will be apparent thatcertain changes and modifications may be practiced within the scope ofthe disclosed embodiments. It should be noted that there are manyalternative ways of implementing the processes, systems, and apparatusof the present embodiments. Accordingly, the present embodiments are tobe considered as illustrative and not restrictive, and the embodimentsare not to be limited to the details given herein.

What is claimed is:
 1. A method, comprising: performing a depositionprocess on a substrate, the deposition process configured to deposit aruthenium layer in a feature on the substrate, the ruthenium layer beingdoped with zinc at an atomic percentage less than approximately 30percent; after depositing the ruthenium layer, annealing the substrate,wherein the annealing is configured to cause migration of the zinc to aninterface at an oxide layer of the substrate, the migration of the zincproducing an adhesive barrier at the interface that inhibitselectromigration of the ruthenium layer.
 2. The method of claim 1,wherein the feature does not include a barrier layer prior to thedeposition of the ruthenium layer.
 3. The method of claim 1, wherein theannealing of the substrate causes bonding of the zinc to oxygen at theinterface to form the barrier.
 4. The method of claim 1, wherein theannealing of the substrate is performed at a temperature less thanapproximately 350 degrees Celsius.
 5. The method of claim 1, wherein thedeposition process is defined by an electroless deposition processconfigured to co-deposit ruthenium and zinc.
 6. The method of claim 1,wherein the feature is a via, and wherein the method defines a pre-filloperation configured to partially fill the via with the ruthenium layer.7. The method of claim 6, wherein the interface is defined along asidewall of the via.
 8. A method, comprising: performing a depositionprocess on a substrate, the deposition process configured to deposit ametallic layer in a feature on the substrate, the metallic layerconsisting of ruthenium doped with zinc at an atomic percentage lessthan approximately 5 percent; after depositing the metallic layer,annealing the substrate, wherein the annealing is configured to causemigration of the zinc to an interface of the metallic layer and an oxidelayer of the substrate, the migration of the zinc producing a barrier atthe interface that inhibits electromigration of the metallic layer. 9.The method of claim 8, wherein the feature does not include a barrierlayer prior to the deposition of the metallic layer.
 10. The method ofclaim 8, wherein the annealing of the substrate causes bonding of thezinc to oxygen at the interface to form the barrier.
 11. The method ofclaim 8, wherein the annealing of the substrate is performed at atemperature less than approximately 350 degrees Celsius.
 12. The methodof claim 8, wherein the deposition process is defined by an electrolessdeposition process.
 13. The method of claim 8, wherein the feature is avia, and wherein the method defines a pre-fill operation configured topartially fill the via with the metallic layer.
 14. The method of claim13, wherein the interface of the metallic layer and the oxide layer isdefined along a sidewall of the via.
 15. A method, comprising:performing a first deposition process on a substrate, the firstdeposition process configured to deposit a ruthenium layer in a featureon the substrate; performing a second deposition process on thesubstrate, the second deposition process configured to deposit aconformal layer of zinc over the ruthenium layer; annealing thesubstrate, wherein the annealing is configured to cause migration of thezinc to an interface at an oxide layer of the substrate, the migrationof the zinc producing a barrier at the interface that inhibitselectromigration of the ruthenium layer.
 16. The method of claim 15,wherein the feature does not include a barrier layer prior to thedeposition of the ruthenium layer.
 17. The method of claim 15, whereinthe annealing of the substrate causes bonding of the zinc to oxygen atthe interface to form the barrier.
 18. The method of claim 15, whereinthe annealing of the substrate is performed at a temperature less thanapproximately 350 degrees Celsius.
 19. The method of claim 15, whereinthe first deposition process is defined by an electroless depositionprocess configured to deposit ruthenium.
 20. The method of claim 15,wherein the feature is a via, and wherein the method defines a pre-filloperation configured to partially fill the via with the ruthenium layer.21. The method of claim 20, wherein the interface is defined along asidewall of the via.